This invention relates to an ink ribbon having sensor marks and adapted to be used for thermal transfer recording. More particularly, it relates to an ink ribbon having sensor marks that can reliably be read in use.
Sublimation type thermal transfer recording methods for forming an image by laying an ink ribbon having ink layers containing sublimating or thermally diffusive dyes and printing paper having a dye receiving layer one on the other, heating the ink layers typically by means of a thermal head according to the image information applied to it and transferring the dyes of the ink layers to the dye receiving layer of the printing paper are known. Such sublimation type thermal transfer recording methods are attracting attention because they can form a full color image with continuously changing color tones particularly in the case of making a hard copy of an image from a video tape.
The sublimation type thermal transfer recording method is used with a printer that is adapted to use an ink ribbon typically provided with sensor marks for placing the ink ribbon in position. Since the sensor marks and the ink layers show respective optical translucent density that are different from each other, the printer using the ink ribbon can detect a sensor mark by way of a change in the translucent density of the ink ribbon to place the latter in position. The sensor marks are required to be reliably read by the sensor of the printer.
The sensor of the printer may be of the transmission type and or of the transmission/reflection type.
Referring to FIGS. 1 and 2 of the accompanying drawings, the sensor of the transmission type has a light emitting section 12 arranged to face the side of an ink ribbon 10 that carries sensor marks 11 and a light receiving section 13 arranged opposite to the light emitting section 12 so as to allow the ink ribbon 10 to pass therebetween.
The light emitting section 12 of the transmission type sensor emits light, which is received by the light receiving section 13. As shown in FIG. 1, light emitted from the light emitting section 12 passes through the ink ribbon 10 in areas other than those of the sensor marks 11 and received by the light receiving section 13. However, the sensor marks 11 block light so that light emitted from the light emitting section 12 cannot pass therethrough. In this way, the transmission type sensor detects each sensor mark 11.
In the case of the transmission/reflection type sensor as shown in FIGS. 3 and 4, a reflector panel 14 is arranged at the side of the ink ribbon 10 opposite to the side that carries sensor marks 11. Both a light emitting section 12 and a light receiving section 13 are arranged opposite to the reflector panel 14 so as to allow the ink ribbon 10 to pass therebetween. The light emitting section 12 and the light receiving section 13 are located at respective positions that are conjugative relative to each other.
Thus, the light emitting section 12 of the transmission/reflection type sensor emit light, which is reflected by the reflector panel 14 and received by the light receiving section 13. As shown in FIG. 3, light emitted from the light emitting section 12 passes through the ink ribbon 10 in areas other than those of the sensor marks 11 and reflected by the reflector panel 14 before it is received by the light receiving section 13. However, the sensor marks 11 block light so that light emitted from the light emitting section 12 cannot pass therethrough. In this way, the transmission/reflection type sensor detects each sensor mark 11.
The reliability of detecting sensor marks 11 of the transmission type sensor can be improved by using thick sensor marks 11.
However, if the sensor marks 11 are too thick, they can be deformed while the ink ribbon 10 is stored for a long period of time as high pressure is applied to them by the parts of the ink ribbon 10 that are held in contact with them.
In view of this problem, it is desirably that the sensor marks 11 has a thickness same as that of the ink layers, which is normally about 2 .mu.m or less. In other words, the sensor marks 11 have to meet both the requirement of a small thickness and that of a high translucent density.
Additionally, in the case of the transmission/reflection type sensor, if the sensor marks 11 show a high surface reflectance, the light receiving section 13 can receive light reflected not by the reflector panel 14 but by the adjacent surface of a sensor mark 11 and mistake the sensor mark 11 for an area other than the sensor mark 11. Then, the sensor mark 11 is not correctly recognized to give rise to misalignment of the ink ribbon 10 and a failure on the part of the printer.
Efforts have been paid to optimize the chemical composition and the thickness of sensor marks 11 in order to optimize the translucent density and the surface reflectance of sensor marks 11. However, the problem of missing sensor marks of the sensor has not been completely eliminated to date.
In view of the above described circumstances, it is therefore the object of the present invention to provide an ink ribbon to be used for thermal transfer recording that shows an improved reliability for detecting sensor marks and can be stored without losing the improved reliability.